CN110075720A - A kind of unleaded BaTiO3- PVDF composite membrane and preparation method thereof - Google Patents

Abstract

The invention discloses a lead-free BaTiO ₃ -PVDF composite film and a preparation method thereof; the lead-free BaTiO ₃ -PVDF composite film contains BaTiO ₃ twins. The preparation method is as follows: use BaTiO ₃ twin powder as raw material; add appropriate amount of BaTiO ₃ twin powder into N,N dimethylformamide solution containing PVDF, mix evenly and spread it on a glass slide, and vacuum After drying and quenching treatment, a BaTiO ₃ twin-PVDF composite film was obtained. The preparation method disclosed by the invention simply and effectively enhances the electromechanical coupling piezoelectric performance of the lead-free BaTiO ₃ -PVDF composite film, and simultaneously enhances its dielectric and ferroelectric performance. The present invention proposes and prepares the BaTiO ₃ twin-PVDF composite film for the first time, which has excellent performance, simple preparation process, and is convenient for large-scale application.

Description

A kind of lead-free BaTiO3-PVDF composite film and preparation method thereof

technical field

The invention relates to the technical field of piezoelectric composite material preparation, and more specifically relates to a lead-free BaTiO ₃ -PVDF composite film and a preparation method thereof.

Background technique

Piezoelectric composite materials are widely used in medical treatment, sensing, measurement and other fields. They are composed of two or more materials. Common piezoelectric composite materials are two-phase composites of piezoelectric ceramics and polymers such as polyvinylidene fluoride or epoxy resins. This composite material combines the advantages of piezoelectric ceramics and polymers, has good flexibility and processability, and has a low density. It is easy to prepare large and uniform films, and is easy to mix with air, water, and organisms. Tissues, etc. to achieve acoustic impedance matching.

In order to make the piezoelectric coefficient of piezoelectric composite materials meet the requirements of use, the common method is to use lead-containing ceramics with large piezoelectric coefficients such as lead zirconate titanate (PZT) ceramics and organic polymer PVDF to prepare composite films, but zirconium Lead titanate contains lead, which seriously pollutes the environment and poses a great threat to human health. Therefore, people use barium titanate (BaTiO ₃ ) which does not contain lead and has a simple structure instead of lead zirconate titanate to prepare BaTiO ₃ -PVDF composite film. However, the piezoelectric coefficient of BaTiO ₃ -PVDF composite film is low and cannot meet the application requirements. .

Therefore, it becomes particularly important to provide a lead-free BaTiO ₃ -PVDF composite film with excellent electrical coupling performance and a preparation method thereof.

SUMMARY OF THE INVENTION

In view of this, the invention provides a lead-free BaTiO ₃ -PVDF composite film with excellent electrical coupling performance and a preparation method thereof. In the present invention, BaTiO ₃ twin powder is used to replace common BaTiO ₃ powder. The electromechanical coupling performance of the designed and prepared composite film is obviously greater than that of common BaTiO ₃ -PVDF composite film, and the dielectric and ferroelectric properties are also significantly improved.

In order to achieve the above object, the present invention adopts the following technical solutions:

The invention discloses a lead-free BaTiO ₃ -PVDF composite film, wherein the lead-free BaTiO ₃ -PVDF composite film contains BaTiO ₃ twin crystals.

As a preferred solution, the present invention is a lead-free BaTiO ₃ -PVDF composite film, in the lead-free BaTiO ₃ -PVDF composite film, the mass percentage of BaTiO ₃ twins is less than or equal to 50% and not equal to 0%, preferably 5-35%, more preferably 20-30%.

The preparation method of a kind of lead-free BaTiO ₃ -PVDF composite film of the present invention comprises the following steps:

BaTiO ₃ twins and PVDF were selected according to the design composition; PVDF and BaTiO ₃ twins were added to the solvent to obtain a suspension; then the suspension was coated on the substrate and dried to obtain a BaTiO ₃ twin-PVDF composite film.

As a preferred solution, a method for preparing a lead-free BaTiO ₃ -PVDF composite film of the present invention, the solvent is selected from at least one of N,N dimethylformamide, dimethylacetamide and N-methylpyrrolidone , preferably N,N dimethylformamide.

As a preferred technical solution, the preparation method comprises the following steps:

(1) Add the prepared PVDF powder into N,N dimethylformamide, and stir magnetically to completely dissolve the PVDF powder to form a transparent viscous solution;

(2) Add the prepared BaTiO ₃ twins to the solution prepared in step (1), then magnetically stir, then ultrasonic, and continue to stir to form a stable suspension;

(3) The suspension is uniformly coated on a glass slide, then the glass slide is put into a vacuum drying oven, vacuumed, and heated to remove the solvent to obtain BaTiO twin _- PVDF composite film;

(4) Put the BaTiO ₃ twinned-PVDF composite film on a heating plate to heat it, then quickly transfer it to an ice-water mixture for quenching treatment, and finally dry to remove the moisture on the surface of the composite film.

As a further preferred solution, in the preparation method of a lead-free BaTiO ₃ -PVDF composite film of the present invention, in step (2), the speed of magnetic stirring is 100-400 rpm; after 60-300 min of magnetic stirring, ultrasonic, ultrasonic Then continue magnetic stirring for 60-300 min to obtain a stable suspension; the ultrasonic time is 10-60 min. Stirring and ultrasound in the step (2) ensure that the BaTiO ₃ twinned powder is uniformly dispersed in the N,N dimethylformamide solution of PVDF.

As a further preferred solution, the present invention provides a method for preparing a lead-free BaTiO ₃ -PVDF composite film. In step (2), the grain size of BaTiO ₃ twins is 10-30 microns.

As a further preferred solution, in the method for preparing a lead-free BaTiO ₃ -PVDF composite film of the present invention, in step (3), vacuumize the furnace until the vacuum degree in the furnace is less than or equal to 133Pa; when heating, control the temperature to 40-80°C. Vacuuming in the step (3) ensures that there are no small pores inside the BaTiO ₃ twinned-PVDF composite membrane, and heating ensures that the solvent N,N dimethylformamide is completely volatilized.

As a further preferred solution, a method for preparing a lead-free BaTiO ₃ -PVDF composite film of the present invention, in step (4), place the BaTiO ₃ twinning-PVDF composite film on a heating plate and heat it to 180-220°C and keep it warm 5-10min; then quenching treatment.

As a further preferred solution, a method for preparing a lead-free BaTiO ₃ -PVDF composite film of the present invention, in step (4), the BaTiO ₃ twinning-PVDF composite film is quenched to obtain a composite of ferroelectric phase β phase with PVDF membrane.

In the exploration process of the present invention, when setting up a control experiment, the BaTiO ₃ twinned powder is replaced with ordinary BaTiO ₃ powder, and steps (1) to (4) are repeated to prepare an ordinary BaTiO ₃ -PVDF composite film.

Preferably, the BaTiO3 twins in the step ( ₁ ) are prepared through the following steps: preparing for the preparation of BaTiO3 twins _- PVDF composite film in advance, specifically including the following steps:

a, take by weighing anatase titanium dioxide powder, sodium hydroxide and potassium hydroxide, mix together and put into the reactor;

b. Put the reaction kettle into the muffle furnace, raise the temperature to 160-220°C for 300-600min, and cool naturally after the reaction;

C, the reactor is taken out, and _BaCl is added dropwise in the reactor Solution;

d. Put the reaction kettle into the muffle furnace, raise the temperature to 160-220°C for 1440-10080 min, and cool naturally after the reaction;

e. Take out the reaction kettle, pour the powder in the reaction kettle into the container, add an appropriate amount of deionized water to the container, stir, let it stand, pour off the supernatant in the beaker, repeat this step until the supernatant in the beaker The pH of the solution is neutral;

f. Add dilute hydrochloric acid dropwise into the beaker and stir until no small bubbles are produced;

g. Add an appropriate amount of deionized water to the beaker, stir, let stand, pour off the supernatant in the beaker, repeat this step until the pH of the supernatant in the beaker is neutral;

h. Take out the powder in the beaker, put it into a constant temperature drying oven, and dry it at 40-80°C.

The present invention prepares for the preparation of BaTiO ₃ twins-PVDF composite film in advance, that is, BaTiO ₃ twins are prepared by the alkali-thermal method, the size is 10-30 μm, preferably 18-25 μm, and the morphology and structure are cubes superimposed and interspersed with each other , the surface is smooth, with sharp edges and corners, which can meet the requirements for preparing BaTiO ₃ twinned-PVDF composite films. The two-step reaction temperature and time used in the present invention will affect the size and morphology of the barium titanate twins, and the BaTiO ₃ twin-PVDF composite film suitable for the preparation can be prepared by adjusting the reaction temperature and time of the first step and the second step The required BaTiO ₃ twin crystal powder, and then achieve the purpose of enhancing the electromechanical coupling performance of BaTiO ₃ twin crystal-PVDF composite film.

Preferably, the XRD phase information of the BaTiO ₃ twin is the same as that of ordinary BaTiO ₃ , which is a tetragonal phase.

Preferably, the BaTiO ₃ twins can also be doped; the doping amount is less than or equal to 50%; preferably 20%-30%.

Principles and advantages

In the present invention, for the first time, BaTiO ₃ twinned powder is substituted for ordinary amorphous BaTiO ₃ powder, and a BaTiO ₃ twinned _- PVDF composite film is designed and prepared. The electromechanical coupling performance of the film is obviously greater than that of ordinary BaTiO ₃ -PVDF composite film, and its dielectric and ferroelectric properties are also significantly improved.

In the BaTiO ₃ twin-PVDF composite film prepared by the invention, the BaTiO ₃ twins are evenly distributed in the PVDF, and the overall thickness is uniform. Among them, the stirring in step (1) ensures that the PVDF powder is completely integrated into the solvent N,N dimethylformamide; the stirring and ultrasonication in step (2) ensure that the BaTiO ₃ twin crystal powder is evenly dispersed into the N,N of PVDF. In the dimethylformamide solution; in the step (3), vacuuming ensures that there is no small air hole in the BaTiO ₃ twinned-PVDF composite membrane, and heating ensures that the solvent N,N dimethylformamide is completely volatilized; step (4) Quenching the BaTiO ₃ twin-PVDF composite film in the process ensures that the composite film has the ferroelectric β phase of PVDF.

The present invention tests the piezoelectric coefficient of the BaTiO ₃ twin-PVDF composite film, characterizes the strength of its electromechanical coupling performance through the piezoelectric coefficient, and also tests the dielectric and ferroelectric properties.

The present invention sets up a control experiment, changes BaTiO ₃ twin powder into ordinary BaTiO ₃ powder, prepares ordinary BaTiO ₃ -PVDF composite film completely according to steps (1) and (2), and tests its dielectric, ferroelectricity and piezoelectricity. electrical properties.

Compared with the ordinary BaTiO ₃ -PVDF composite film, the BaTiO ₃ twin-PVDF composite film designed and prepared by the present invention has significantly enhanced electromechanical coupling performance, and also significantly enhanced dielectric and ferroelectric properties.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only It is an embodiment of the present invention, and those skilled in the art can also obtain other drawings according to the provided drawings without creative work.

Fig. 1 accompanying drawing is a flow chart of enhancing the electromechanical coupling performance of the lead-free BaTiO ₃ -PVDF composite film disclosed by the present invention;

Accompanying drawing of Fig. 2 is the BaTiO that embodiment 1 prepares ₃ Twin SEM figure;

Accompanying drawing of Fig. 3 is the SEM picture of the BaTiO that embodiment ₁ prepares twin-PVDF composite film;

Accompanying drawing of Fig. ₄ is the XRD figure of the BaTiO3 twin crystal-PVDF composite film that embodiment 1 prepares;

Fig. 5 accompanying drawing is the dielectric constant and the dielectric loss diagram of the BaTiO ₃ twin-PVDF composite film and common BaTiO ₃ -PVDF composite film prepared in Example 1;

Fig. 6 accompanying drawing is the electrical hysteresis loop diagram of BaTiO ₃ twin crystal-PVDF composite film and ordinary BaTiO ₃ -PVDF composite film prepared in embodiment 1;

Figure 7 is a graph showing the piezoelectric coefficients of the BaTiO ₃ twinned-PVDF composite film prepared in Example 1 and the common BaTiO ₃ -PVDF composite film.

Detailed ways

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

Example 1

In this embodiment, a lead-free BaTiO ₃ -PVDF composite film, setting the doping mass fraction of the composite film to 20%, includes the following steps:

(1) BaTiO ₃ twin crystal powder is prepared by alkali-thermal method, which specifically includes the following steps:

A, take by weighing anatase titanium dioxide powder 0.039g, sodium hydroxide 3.877g, potassium hydroxide 5.122g, mix together and put into the reactor;

b. Put the reaction kettle into the muffle furnace, keep it warm at 180°C for 300min, and cool it naturally;

c, the reaction kettle is taken out, and 2ml concentration is added dropwise in the reaction kettle to be the _BaCl of 0.3mol/L solution;

d. Put the reaction kettle into the muffle furnace, keep it warm at 180°C for 2880min, and cool it naturally;

e. Take out the reaction kettle, pour the powder in the reaction kettle into a beaker, add an appropriate amount of deionized water to the beaker, stir for 5 minutes, let it stand for 20 minutes, pour off the supernatant in the beaker, and repeat this step until the The pH of the supernatant is neutral;

f. Add 1% dilute hydrochloric acid dropwise to the beaker and stir until no small bubbles are produced;

g. Add an appropriate amount of deionized water to the beaker, stir for 5 minutes, let it stand for 20 minutes, pour off the supernatant in the beaker, and repeat this step until the pH of the supernatant in the beaker is neutral;

h. Take out the powder in the beaker, put it into a constant temperature drying oven, and dry it at 60° C. for 600 minutes to obtain BaTiO ₃ twin crystal powder.

(2) Add the above-mentioned BaTiO ₃ twin crystal powder prepared by the alkali-thermal method into the N,N dimethylformamide solution of PVDF, mix evenly and spread it on a glass slide, dry it in vacuum, and then perform quenching treatment , to obtain the BaTiO twin _- PVDF composite film, which specifically includes the following steps:

(a) Weigh 1g of PVDF powder and add it to 10ml of N,N dimethylformamide, stir magnetically for 5 hours to completely dissolve the PVDF powder and form a transparent viscous solution;

(b) Weigh 0.25 g of BaTiO ₃ twins and add them to the solution prepared in step (a), then magnetically stir for 300 min, then ultrasonically for 60 min, and continue stirring for 300 min to form a stable suspension;

(c) Evenly coat the suspension on a glass slide, then place the glass slide in a vacuum drying oven, vacuumize, and keep warm at 60°C for 240min to remove the solvent to obtain a BaTiO ₃ twinned-PVDF composite film;

(d) Heat the BaTiO ₃ twinned-PVDF composite film on a heating plate at 200°C for 7 minutes, quickly transfer it to an ice-water mixture at 0°C, and finally dry it at 60°C to remove the moisture on the surface of the composite film.

(3) Dielectric, ferroelectric and piezoelectric tests are carried out on the BaTiO ₃ twinned-PVDF composite film prepared in the above step (2), specifically including the following steps:

(A) Gold-plated point electrodes on the BaTiO ₃ twinned-PVDF composite film with an area of 2.54 mm ² ;

(B) Agilent 4294A LCR impedance analyzer and RADIANT Precision Premier II ferroelectric analyzer were used to test the dielectric and ferroelectric properties of the BaTiO ₃ twinned-PVDF composite film, respectively;

(C) Polarize the BaTiO ₃ twinned-PVDF composite film, the polarization temperature is 80°C, the polarization electric field is 4kV/mm, and the polarization time is 40min;

(D) The piezoelectric coefficient of the polarized BaTiO ₃ twinned-PVDF composite film was tested using a quasi-static d33 measuring instrument, and the piezoelectric coefficients of five samples with the same doping mass fraction were measured.

At the same time, according to the above steps, a BaTiO ₃ (non-twinned)-PVDF composite film with a doping mass fraction of 20% was prepared and tested using ordinary BaTiO ₃ powder as a control group.

Example 2

In this embodiment, a lead-free BaTiO ₃ -PVDF composite film, setting the doping mass fraction of the composite film to 30%, includes the following steps:

(1) BaTiO ₃ twin crystal powder is prepared by alkali-thermal method, which specifically includes the following steps:

A, take by weighing anatase titanium dioxide powder 0.039g, sodium hydroxide 3.877g, potassium hydroxide 5.122g, mix together and put into the reactor;

b. Put the reaction kettle into the muffle furnace, keep it warm at 180°C for 300min, and cool it naturally;

c, the reaction kettle is taken out, and 2ml concentration is added dropwise in the reaction kettle to be the _BaCl of 0.3mol/L solution;

d. Put the reaction kettle into the muffle furnace, keep it warm at 180°C for 2880min, and cool it naturally;

e. Take out the reaction kettle, pour the powder in the reaction kettle into a beaker, add an appropriate amount of deionized water to the beaker, stir for 5 minutes, let it stand for 20 minutes, pour off the supernatant in the beaker, and repeat this step until the The pH of the supernatant is neutral;

f. Add 1% dilute hydrochloric acid dropwise to the beaker and stir until no small bubbles are produced;

g. Add an appropriate amount of deionized water to the beaker, stir for 5 minutes, let it stand for 20 minutes, pour off the supernatant in the beaker, and repeat this step until the pH of the supernatant in the beaker is neutral;

h. Take out the powder in the beaker, put it into a constant temperature drying oven, and dry it at 60° C. for 600 minutes to obtain BaTiO ₃ twinned powder.

(2) Add the above-mentioned BaTiO ₃ twin crystal powder prepared by the alkali-thermal method into the N,N dimethylformamide solution of PVDF, mix evenly and spread it on a glass slide, dry it in vacuum, and then perform quenching treatment , to obtain the BaTiO twin _- PVDF composite film, which specifically includes the following steps:

(a) Weigh 1g of PVDF powder and add it to 10ml of N,N dimethylformamide, stir magnetically for 5 hours to completely dissolve the PVDF powder and form a transparent viscous solution;

(b) Weigh 0.428g of BaTiO ₃ twins and add them to the solution prepared in step (a), then magnetically stir for 300min, then sonicate for 60min, and continue stirring for 300min to form a stable suspension;

(c) Evenly coat the suspension on a glass slide, then place the glass slide in a vacuum drying oven, vacuumize, and keep warm at 60°C for 240min to remove the solvent to obtain a BaTiO ₃ twinned-PVDF composite film;

(d) Heat the BaTiO ₃ twinned-PVDF composite film on a heating plate at 200°C for 7 minutes, quickly transfer it to an ice-water mixture at 0°C, and finally dry it at 60°C to remove the moisture on the surface of the composite film.

( ₃ ) Conduct dielectric, ferroelectric and piezoelectric tests on the BaTiO twin-PVDF composite film prepared in the above step (2), specifically including the following steps:

(A) Gold-plated point electrodes on both sides of the BaTiO ₃ twinned-PVDF composite film, with an area of 2.54mm ² ;

(B) Agilent 4294A LCR impedance analyzer and RADIANT Precision Premier II ferroelectric analyzer were used to test the dielectric and ferroelectric properties of the BaTiO ₃ twinned-PVDF composite film, respectively;

(C) Polarize the BaTiO ₃ twinned-PVDF composite film, the polarization temperature is 80°C, the polarization electric field is 4kV/mm, and the polarization time is 40min;

(D) Piezoelectric coefficients of polarized BaTiO ₃ twinned-PVDF composite films were measured using a quasi-static d33 measuring instrument. The piezoelectric coefficients of five samples with the same doping mass fraction were measured.

At the same time, according to the above steps, a BaTiO ₃ -PVDF composite film with a doping mass fraction of 20% was prepared and tested using ordinary BaTiO ₃ powder as a control group.

As shown in Figure 2, the morphology and structure of BaTiO ₃ twins are cubes stacked and interspersed with each other, the grain size is about 20um, and the grain surface is smooth with sharp edges and corners.

As shown in Figure 3, it can be clearly seen that BaTiO ₃ twins are evenly distributed in PVDF. One plane of BaTiO ₃ twins tends to face outward, and few corners face outward. This arrangement follows the principle of the lowest energy.

As shown in Figure 4, it can be clearly seen from XRD that the BaTiO ₃ twins-PVDF composite film has both the BaTiO ₃ twins and the diffraction peaks of PVDF, and the BaTiO ₃ twins in the composite film have the same diffraction peaks as the BaTiO ₃ standard card. Corresponding; after quenching treatment, the composite membrane has α and β phases of PVDF.

As shown in Figure 5, it can be clearly seen that the dielectric constant of the BaTiO ₃ twinned-PVDF composite film is significantly greater than that of the BaTiO ₃ -PVDF composite film, and the dielectric constant value is about 25 when the frequency is 1000 Hz.

As shown in Figure 6, it can be clearly seen that the ferroelectric properties of the BaTiO ₃ twinned-PVDF composite film are significantly greater than that of the BaTiO _{3 -PVDF} composite film. When the electric field is 200kV/mm, the remaining The polarization value is 4.42uC/cm ² , and the saturation polarization value is 8.99 uC/cm ² .

As shown in Figure 7, it can be clearly seen that the piezoelectric coefficient of the BaTiO ₃ twinned-PVDF composite film is significantly greater than that of the BaTiO ₃ -PVDF composite film, indicating that the electromechanical coupling performance of the BaTiO ₃ twinned-PVDF composite film is greater than that of BaTiO ₃ - The PVDF composite film further shows that the present invention really enhances the electromechanical coupling performance of the lead-free BaTiO ₃ -PVDF composite film.

The present invention also explores BaTiO ₃ twin-PVDF composite films (such as 5%, 8%, 10%, 40%, 50%) of other doping mass fractions and common BaTiO ₃ -PVDF composite films corresponding to the same doping amount In general, the electromechanical coupling performance of the BaTiO ₃ twinned-PVDF composite film with doping mass fractions of 20% and 30% is relatively large, which has achieved unexpected results.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. a kind of unleaded BaTiO₃- PVDF composite membrane, it is characterised in that: the unleaded BaTiO₃Contain in-PVDF composite membrane BaTiO₃Twin.

2. a kind of unleaded BaTiO according to claim 1₃- PVDF composite membrane, it is characterised in that: the unleaded BaTiO₃- In PVDF composite membrane, BaTiO₃The mass percent of twin is greater than 0% and is less than or equal to 50%, preferably 5-35%, further excellent It is selected as 20-30%.

3. a kind of prepare the unleaded BaTiO as described in claim 1-2 any one₃The method of-PVDF composite membrane, it is characterised in that Include the following steps:

Match by design component and takes appropriate BaTiO₃Twin and PVDF；By PVDF and BaTiO₃Twin is added in solvent and is suspended Liquid；Then by suspension in substrate, and it is dried to obtain BaTiO₃Twin-PVDF composite membrane.

4. a kind of unleaded BaTiO according to claim 3₃The preparation method of-PVDF composite membrane；It is characterized by: described molten Agent is selected from least one of n,N dimethylformamide, dimethyl acetamide and N-Methyl pyrrolidone, preferably N, N diformazan Base formamide.

5. a kind of unleaded BaTiO according to claim 4₃The preparation method of-PVDF composite membrane；It is characterized in that；The system Preparation Method includes the following steps:

(1) it will be added in n,N dimethylformamide with the PVDF powder taken, magnetic agitation is completely dissolved PVDF powder, shape At clear viscous shape solution；

It (2) will be with the BaTiO taken₃Twin powder is added in the solution of step (1) preparation, then magnetic agitation, then ultrasound, after Continuous stirring, forms stable suspension；

(3) uniform suspension is coated on glass slide, then glass slide is put into vacuum oven, vacuumized, heating with Solvent is removed, BaTiO is obtained₃Twin-PVDF composite membrane；

(4) by BaTiO₃After twin-PVDF composite membrane puts heating on hot plate, it is transferred in mixture of ice and water and is quenched, Finally dry removal composite film surface moisture.

6. a kind of unleaded BaTiO according to claim 5₃The preparation method of-PVDF composite membrane；It is characterized by: step (2) in, the speed of magnetic agitation is that 100-400 turns/min；Ultrasound is carried out after magnetic agitation 60-300min, is further continued for after ultrasound Magnetic agitation 60-300min obtains stable suspension；The time of the ultrasound is 10-60min.

7. a kind of unleaded BaTiO according to claim 5₃The preparation method of-PVDF composite membrane, it is characterised in that: step (2) in, BaTiO₃The granularity of twin powder is 10-30 μm.

8. a kind of unleaded BaTiO according to claim 5₃The preparation method of-PVDF composite membrane, it is characterised in that: in step (3) it in, is evacuated to vacuum degree in furnace and is less than or equal to 133Pa；When heating, controlled at 40-80 DEG C.

9. a kind of unleaded BaTiO according to claim 5₃The preparation method of-PVDF composite membrane, it is characterised in that: in step (4) in, by BaTiO₃Twin-PVDF composite membrane is put be heated to 180-220 DEG C on hot plate after keep the temperature 5-10min；Then into Row quenching treatment；Obtain the composite membrane with PVDF ferroelectricity β phase.

10. a kind of unleaded BaTiO according to claim 7₃The preparation method of-PVDF composite membrane, it is characterised in that: step (2) BaTiO described in₃Twin is prepared by following step:

A. appropriate rutile titanium dioxide powder, sodium hydroxide powder and potassium hydroxide powder are weighed, mixes and is put into instead It answers in kettle；

B. reaction kettle is put into Muffle furnace, is warming up to 160-220 DEG C of reaction 300-600min, then cooled to room temperature；

C. reaction kettle is taken out, BaCl is added dropwise into reaction kettle₂Solution；

D. reaction kettle is put into Muffle furnace, is warming up to 160-220 DEG C of reaction 1440-10080min, natural cooling after reaction；

E. reaction kettle is taken out, the powder in reaction kettle is poured into container, into container plus appropriate amount of deionized water, stirring are quiet It sets, removes supernatant in beaker, repeat this step, until the supernatant pH value in beaker is 7 or so；

F. dilute hydrochloric acid is added dropwise into beaker and stirs, until bubble-free generates；

G. add appropriate amount of deionized water into beaker, stir, stand, remove supernatant in beaker, repeat this step, until in beaker Supernatant pH value be 7 or so；

H. the powder in beaker is taken out, thermostatic drying chamber is put into, in 40-80 DEG C of drying.